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๐Ÿ‡ฉ๐Ÿ‡ช enterJS 2024

๐Ÿ‡ฉ๐Ÿ‡ช enterJSย 2024

Web performance APIs you (probably) didn't know existed

Responsiveness to interaction is crucial for our apps and youโ€™ve probably heard about the amazing tools we have to measure web performance. But did you know there are many performance APIs native to the Web Platform?

In this talk, weโ€™ll see how to leverage the power of some of them to reliably measure responsiveness and correctly identify culprits for bad experiences.

Matheus Albuquerque

May 08, 2024
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  1. Matheus Albuquerque โ† ๐• ythecombinator โ† ๐Ÿ‘จ๐Ÿ’ป Sr. SWE @

    Medallia โ† โšก Google Developer Expert โ† โš› PC @ React Su m m it NYC โ† ๐Ÿง‘๐Ÿซ Mentor @ TechLabs
  2. Matheus Albuquerque โ† ๐• ythecombinator โ† ๐Ÿ‘จ๐Ÿ’ป Sr. SWE @

    Medallia โ† โšก Google Developer Expert โ† โš› PC @ React Su m m it NYC โ† ๐Ÿง‘๐Ÿซ Mentor @ TechLabs โ†‘ ALL THE LINKS!
  3. YOU ALREADY KNOWโ€ฆ โ† HTTP/2 โ† COMPRESS JAVASCRIPT (E.G. WITH

    BROTLI/ZSTD) AND USE IMAGE CDNS (40โ€“80% SAVINGS) โ† OPTIMIZE THIRD-PARTIES (DEFER/REPLACE/UPDATE THEM) โ† WORKERS TO OFF-LOAD THE MAIN THREAD
  4. This talk presents Why am I here? Measuring Measuring (with

    the platform) Optimizing (with the platform) Why are we here? Closing thoughts
  5. This talk presents Why am I here? Measuring Measuring (with

    the platform) Optimizing (with the platform) Why are we here? Closing thoughts
  6. #QUESTION ๐Ÿค” What does it mean to be fast? If

    you were to summarize web performance in one metric, whatโ€™d be your pick?
  7. #QUESTION ๐Ÿค” What does it mean to be fast? If

    you were to summarize web performance in one metric, whatโ€™d be your pick? e.g. load time, responsiveness, etc.
  8. #PROTIP๐Ÿ’ก A lot of loading metrics don't capture user experience.

    We need to think about our metrics in terms of what matters.
  9. #QUESTION ๐Ÿค” What does it mean to be fast? If

    you were to summarize web performance in one metric, whatโ€™d be your pick?
  10. WHAT DOES IT MEAN TO BE FAST? PERCEIVED LOAD SPEED

    HOW QUICKLY A PAGE CAN LOAD AND RENDER ALL OF ITS VISUAL ELEMENTS TO THE SCREEN LOAD RESPONSIVENESS HOW QUICKLY A PAGE CAN LOAD/RUN ANY REQUIRED JS IN ORDER FOR COMPONENTS TO RESPOND TO USER INTERACTION RUNTIME RESPONSIVENESS AFTER THE PAGE LOAD, HOW QUICKLY CAN THE PAGE RESPOND TO USER INTERACTION? SMOOTHNESS DO TRANSITIONS & ANIMATIONS RENDER AT A CONSISTENT FRAME RATE AND FLOW FLUIDLY?
  11. #PROTIP๐Ÿ’ก The only way to truly know how your site

    performs for your users is to actually measure its performance as those users are loading and interacting with it.
  12. JEAN-ANTOINE NOLLET โ† THE FIRST EVER RUM EXPERIMENT IN 1746

    โ† HE GATHERED หœ200 MONKS IN CIRCUMFERENCE, WIRED USING IRON, AND DISCHARGED A BATTERY THROUGH THE HUMAN CHAIN โ† HE WAS TESTING THE LATENCY OF AN ELECTRIC SIGNAL WITH REAL USERS
  13. #PROTIP๐Ÿ’ก Browsers now provide us with many apis to fetch

    performance metrics that help site owners make sites faster.
  14. MEASUREMENT APIS GENERAL STUFF DOMHighResTimeStamp, PerformanceObserver, PAGE VISIBILITY API &

    LAYOUT INSTABILITY API PROFILING LONG TASKS API, UserAgentSpecificMemory & JS SELF- PROFILING API TIMING USER TIMING, ELEMENT TIMING. EVENT TIMING, RESOURCE TIMING, NAVIGATION TIMING & SERVER TIMING SENSORS BATTERY STATUS & NETWORK INFORMATION
  15. #1 PAGE VISIBILITY โ† CANCEL NETWORK REQUESTS AND OTHER TIME-BASED

    EVENTS โ† FETCH INCOMPLETE MEDIA OR DOWNLOAD THE REST OF YOUR BUNDLES USING DYNAMIC IMPORTS โ† PAUSE VIDEOS AND CAROUSELS, IF THE USER IS NOT WATCHING THEM
  16. #2 PerformanceObserver โ† SUBSCRIBE TO PERFORMANCE-RELATED EVENTS โ† CALLBACKS ARE

    GENERALLY FIRED DURING IDLE PERIODS โ† YOU TELL THE OBSERVER WHAT TYPES OF ENTRIES TO LISTEN FOR
  17. #2 PerformanceObserver const observer = new PerformanceObserver((list) = > {

    for (const entry of list.getEntries()) { console.log(entry.toJSON()); } }); observer.observe({type: 'some-entry-type'});
  18. #3 LAYOUT INSTABILITY โ† MANY WEBSITES HAVE DOM ELEMENTS SHIFTING

    AROUND DUE TO CONTENT LOADING ASYNCHRONOUSLY โ† THIS API GIVES US A LIST OF ALL LAYOUT SHIFT EVENTS ON A PAGE
  19. #3 LAYOUT INSTABILITY const observer = new PerformanceObserver((list) = >

    { const entries = list.getEntries(); / / Shifts that are not preceded by input events const nonInputEntries = entries.filter((entry) = > !entry.hadRecentInput); for (const entry of nonInputEntries) { console.log(entry); } }); observer.observe({type: 'layout-shift'});
  20. TIMING โ€” ACT I USER TIMING ALLOWS YOU TO MARK

    POINTS IN TIME AND THEN MEASURE THE DURATION BETWEEN THOSE MARKS. EVENT TIMING EVENT PROCESSING TIME + TIME UNTIL THE NEXT FRAME CAN BE RENDERED. THE BASIS FOR THE FID METRIC. ELEMENT TIMING MEASURE THE RENDER TIME OF SPECIFIC ELEMENTS. THE BASIS FOR THE LCP METRIC.
  21. #1 USER TIMING / / Record the time i m

    m ediately before running a task performance.mark('myTask:start'); await doMyTask(); / / Record the time i m m ediately after running a task performance.mark('myTask:end'); / / Measure the delta between the start and end of the task performance.measure('myTask', 'myTask:start', โ€˜myTask:end'); observer.observe({type: 'measure'});
  22. #1 USER TIMING โ€” TOOLS โ€” "USER TIMING AND CUSTOM

    METRICS" BY STEVE SOUDERS โ€” "USER TIMING AND CUSTOM METRICS" BY STEVE SOUDERS
  23. #2 ELEMENT TIMING โ† ALLOWS YOU TO MEASURE THE RENDER

    TIME OF SPECIFIC ELEMENTS โ† USEFUL FOR KNOWING WHEN THE LARGEST IMAGE OR TEXT BLOCK WAS PAINTED TO THE SCREEN โ† THE BASIS FOR THE LARGEST CONTENTFUL PAINT (LCP) METRIC
  24. #2 ELEMENT TIMING โ† USEFUL TO MEASURE THE EVENT PROCESSING

    TIME AS WELL AS THE TIME UNTIL THE NEXT FRAME CAN BE RENDERED โ† EXPOSES A NUMBER OF TIMESTAMPS IN THE EVENT LIFECYCLE โ† THE BASIS FOR THE FIRST INPUT DELAY METRIC
  25. #3 EVENT TIMING const observer = new PerformanceObserver((entryList) = >

    { const firstInput = entryList.getEntries()[0]; const firstInputDelay = firstInput.processingStart - firstInput.startTime; / / Measure the time it takes to run all event handlers const firstInputProcessingTime = firstInput.processingEnd - firstInput.processingStart; / / Measure the entire duration of the event const firstInputDuration = firstInput.duration; }); observer.observe({type: 'first-input'});
  26. #3 EVENT TIMING MEASURE THE LATENCYโ€ฆ โ† FROM A CLICK

    UNTIL WE REORDER CONTENT ON A TABLE โ† TO DRAG A SLIDER TO FILTER SOME DATA โ† FOR A FLYOUT TO APPEAR WHEN HOVERING A MENU ITEM
  27. PROFILING LONG TASKS API REPORTS TASKS THAT TAKES LONGER THAN

    50 MS AND IT'S THE BASIS FOR TTI AND TBT METRICS JS SELF-PROFILING API PROFILE SPECIFIC COMPLEX OPERATIONS AND IDENTIFY HOT SPOTS USING A SAMPLING PROFILER UserAgentSpecificMemory DETECT MEMORY LEAKS IN APPS THAT HANDLE A HUGE VOLUME OF DATA
  28. #1 LONG TASKS โ† REPORTS TASKS THAT TAKES LONGER THAN

    50 MS โ† USEFUL TO TRACK WHEN THE BROWSER'S MAIN THREAD IS BLOCKED โ† THE BASIS FOR TIME TO INTERACTIVE (TTI) AND TOTAL BLOCKING TIME (TBT) METRICS
  29. #1 LONG TASKS โ€” SPOT observer.observe({type: 'longtask'}); { name: "same-origin-descendant",

    entryType: "longtask", startTime: 1023.40999995591, duration: 187.19000002602115, attribution: [ { name: "unknown", entryType: "taskattribution", startTime: 0, duration: 0, containerType: "iframe", containerSrc: "child.html", containerId: "", containerName: "child1" } ] };
  30. #2 JS SELF - PROFILING const profiler = new Profiler({

    sampleInterval: 10, maxBufferSize: 10000 }); / / Do work . . . const trace = await profiler.stop(); sendProfile(trace);
  31. #2 JS SELF - PROFILING โ† PROFILE SPECIFIC COMPLEX OPERATIONS

    โ† PROFILE THIRD-PARTY SCRIPTS โ† COMBINE WITH OTHER EVENTS/IMPORTANT METRICS, LIKE LONG TASKS OR EVENT TIMING APIS
  32. #3 UserAgentSpecificMemory โ† MEASURES THE MEMORY USAGE AND DETECTS MEMORY

    LEAKS โ† WAITS FOR THE NEXT GC AND THEN MEASURES MEMORY IMMEDIATELY AFTER THE UNNEEDED MEMORY HAS BEEN RELEASED โ† FORCES GC IF IT DOES NOT HAPPEN FOR 20S
  33. MEMORY LEAKS โ† FORGETTING TO UNREGISTER AN EVENT LISTENER โ†

    ACCIDENTALLY CAPTURING OBJECTS FROM AN IFRAME โ† NOT CLOSING A WORKER โ† ACCUMULATING OBJECTS IN ARRAYS
  34. MEMORY LEAKS const obj = { a: new Array(1000), b:

    new Array(2000) }; setInterval(() = > { console.log(obj.a); }, 1000);
  35. { name: "same-origin-descendant", entryType: "longtask", startTime: 1023.40999995591, duration: 187.19000002602115, attribution:

    [ { name: "unknown", entryType: "taskattribution", startTime: 0, duration: 0, containerType: "iframe", containerSrc: "child.html", containerId: "", containerName: "child1" } ] } { bytes: 1000000, breakdown: [ { bytes: 1000000, attribution: [ { url: "https://example.com", scope: "Window", }, ], types: ["JS", "DOM"], }, { bytes: 0, attribution: [], types: [], }, ], } { "frames": [ { "name": "Profiler" }, { "column": 0, "line": 100, "name": "", "resourceId": 0 }, { "name": "set innerHTML" }, { "column": 10, "line": 10, "name": "A", "resourceId": 1 } { "column": 20, "line": 20, "name": "B", "resourceId": 1 } ], "resources": [ "https://example.com/page", "https://example.com/app.js", ], "samples": [ { "stackId": 0, "timestamp": 161.99500000476837 }, { "stackId": 2, "timestamp": 182.43499994277954 }, { "timestamp": 197.43499994277954 }, { "timestamp": 213.32999992370605 }, { "stackId": 3, "timestamp": 228.59999990463257 }, ], "stacks": [ { "frameId": 0 }, { "frameId": 2 }, { "frameId": 3 }, { "frameId": 4, "parentId": 2 } ] } LONG TASKS SELF-PROFILING USERAGENT MEMORY
  36. TIMING โ€” ACT II RESOURCE TIMING RETRIEVE AND ANALYZE DETAILED

    NETWORK TIMING DATA REGARDING THE LOADING SERVER TIMING COMMUNICATE PERFORMANCE METRICS ABOUT HOW TIME IS SPENT WHILE PROCESSING THE REQUEST NAVIGATION TIMING COMPLETE TIMING INFORMATION FOR NAVIGATION OF A DOCUMENT
  37. #1 RESOURCE TIMING const observer = new PerformanceObserver((list) = >

    { for (const entry of list.getEntries()) { / / If transferSize is 0, the resource was fulfilled via the cache. console.log(entry.name, entry.transferSize === 0); } }); observer.observe({type: 'resource'});
  38. #2 NAVIGATION TIMING const observer = new PerformanceObserver((list) = >

    { for (const entry of list.getEntries()) { console.log('Time to first byte', entry.responseStart); } }); observer.observe({type: 'navigation'});
  39. #2 NAVIGATION TIMING / / ServiceWorker startup time const workerStartupTime

    = entry.responseStart - entry.workerStart; / / Request time only (excluding redirects, DNS, and connection/TLS time) const requestTime = entry.responseStart - entry.requestStart; / / Response time only (download) const responseTime = entry.responseEnd - entry.responseStart; / / Request + response time const requestResponseTime = entry.responseEnd - entry.requestStart;
  40. #3 SERVER TIMING MEASURE ANY WORK THAT THE SERVER DOES

    TO COMPLETE A REQUEST: โ† ROUTING/AUTHENTICATING THE REQUEST โ† RUNNING CONTENT THROUGH TEMPLATING SYSTEMS โ† QUERYING DATABASES/API CALLS TO THIRD-PARTY SERVICES
  41. SENSORS BATTERY STATUS INFORMATION ABOUT THE POWER SOURCE, CHARGE LEVEL,

    AND OTHERS NETWORK INFORMATION ADAPT THE USERSโ€™ EXPERIENCE BASED ON THE QUALITY OF THEIR CONNECTION
  42. #1 BATTERY STATUS const batteryInfo = await navigator.getBattery(); batteryInfo.addEventListener("chargingchange", listener);

    batteryInfo.addEventListener("chargingtimechange", listener); batteryInfo.addEventListener("dischargingtimechange", listener); batteryInfo.addEventListener("levelchange", listener);
  43. #2 NETWORK INFORMATION โ† SWITCH BETWEEN SERVING HIGH/LOW DEFINITION CONTENT

    BASED ON THE USER'S NETWORK โ† DECIDE WHETHER TO PRELOAD RESOURCES โ† DEFER UPLOADS/DOWNLOADS WHEN USERS ARE ON A SLOW CONNECTION โ† ADAPT TO SITUATIONS WHEN USERS ARE OFFLINE
  44. #2 NETWORK INFORMATION switch (connectionType) { case "4g": return <Video

    src={videoSrc} />; case "3g": return <Image src={imageSrc.hiRes} alt={alt} />; default: return <Image src={imageSrc.lowRes} alt={alt} />; }
  45. RESOURCE HINTS โ† MANY PERFORMANCE OPTIMIZATIONS CAN BE MADE WHEN

    WE CAN PREDICT WHAT USERS MIGHT DO. โ† RESOURCE HINTS ARE A SIMPLE BUT EFFECTIVE WAY TO ALLOW DEVELOPERS TO HELP THE BROWSER TO STAY ONE STEP AHEAD OF THE USER AND KEEP PAGES FAST.
  46. RESOURCE HINTS < ! - - Preconnect - - >

    <link rel="preconnect" href="https://fonts.gstatic.com"> <link rel="preconnect" href="https://scripts.example.com"> < ! - - Preloading - - > <link rel="preload" href="https://example.com/fonts/font.woff"> < ! - - DNS Prefetch - - > <link rel="dns-prefetch" href="https://fonts.gstatic.com"> <link rel="dns-prefetch" href="https://images.example.com"> < ! - - Prefetch - - > <link rel="prefetch" href="/uploads/images/pic.png"> <link rel="prefetch" href="https://example.com/news/?page=2"> < ! - - Prerender - - > <link rel="prerender" href="https://example.com/news/?page=2">
  47. RESOURCE HINTS < ! - - Preconnect - - >

    <link rel="preconnect" href="https://fonts.gstatic.com"> <link rel="preconnect" href="https://scripts.example.com"> < ! - - Preloading - - > <link rel="preload" href="https://example.com/fonts/font.woff"> < ! - - DNS Prefetch - - > <link rel="dns-prefetch" href="https://fonts.gstatic.com"> <link rel="dns-prefetch" href="https://images.example.com"> < ! - - Prefetch - - > <link rel="prefetch" href="/uploads/images/pic.png"> <link rel="prefetch" href="https://example.com/news/?page=2"> < ! - - Prerender - - > <link rel="prerender" href="https://example.com/news/?page=2">
  48. PRECONNECT โ† IT ALLOWS THE BROWSER TO SETUP EARLY CONNECTIONS

    BEFORE THE REQUEST IS ACTUALLY SENT TO THE SERVER. THIS INCLUDES: โ€ข TLS NEGOTIATIONS โ€ข TCP HANDSHAKES โ† ELIMINATES ROUNDTRIP LATENCY
  49. PRECONNECT 100MS 200MS 300MS 400MS 500MS 600MS 700MS HTML CSS

    FONT 1 FONT 2 FONTS START LOADING FONTS RENDERED
  50. PRECONNECT 100MS 200MS 300MS 400MS 500MS 600MS 700MS HTML CSS

    FONT 1 FONT 2 FONTS START LOADING FONTS RENDERED FONT 1 FONT 2
  51. โ€ฆAND MUCH MORE! โ† DNS PREFETCH โ‡ข WARNS THE BROWSER

    ABOUT THE DOMAINS ITโ€™S GOING TO NEED TO LOOK UP โ† PREFETCH โ‡ข FETCH RESOURCES IN THE BACKGROUND AND STORE THEM IN CACHE โ† PRERENDER โ‡ข IT GOES ONE STEP FURTHER AND EXECUTES THE FILES
  52. PRIORITY HINTS โ† INCREASE THE PRIORITY OF THE LCP IMAGE

    โ† LOWER THE PRIORITY OF ABOVE-THE-FOLD IMAGES AND PRELOADED RESOURCES โ† LOWER THE PRIORITY FOR NON-CRITICAL DATA FETCHES โ† REPRIORITIZE SCRIPTS
  53. PRIORITY HINTS < ! - - Increase the priority of

    the LCP image - - > <img src="image.jpg" fetchpriority="high" /> < ! - - Lower the priority of above-the-fold images - - > <ul class="carousel"> <img src="img/carousel-1.jpg" fetchpriority="high" /> <img src="img/carousel-2.jpg" fetchpriority="low" /> <img src="img/carousel-3.jpg" fetchpriority="low" /> </ul> < ! - - Reprioritize scripts - - > <script src="async_but_important.js" async fetchpriority="high"></script> <script src="blocking_but_unimportant.js" fetchpriority="low"></script>
  54. PRIORITY HINTS < ! - - Increase the priority of

    the LCP image - - > <img src="image.jpg" fetchpriority="high" /> < ! - - Lower the priority of above-the-fold images - - > <ul class="carousel"> <img src="img/carousel-1.jpg" fetchpriority="high" /> <img src="img/carousel-2.jpg" fetchpriority="low" /> <img src="img/carousel-3.jpg" fetchpriority="low" /> </ul> < ! - - Reprioritize scripts - - > <script src="async_but_important.js" async fetchpriority="high"></script> <script src="blocking_but_unimportant.js" fetchpriority="low"></script>
  55. PRIORITY HINTS / / Important validation data const user =

    await fetch("/user"); / / Less important content data const relatedPosts = await fetch("/posts/suggested", { priority: "low" });
  56. PRIORITY HINTS / / Important validation data const user =

    await fetch("/user"); / / Less important content data const relatedPosts = await fetch("/posts/suggested", { priority: "low" });
  57. RESPONSIVE IMAGES โ† IMAGES FOR DESKTOP AND TABLET CAN BE

    หœ2-4X LARGER THAN THE MOBILE ONES. โ† WITH srcset, THE BROWSER WON'T DOWNLOAD THE LARGER IMAGES UNLESS THEY'RE NEEDED. THAT SAVES BANDWIDTH.
  58. RESPONSIVE IMAGES <img src="enterJS.png" srcset=" enterJS-300.png 300w, enterJS-600.png 600w, enterJS-1200.png

    1200w " /> <img src="enterJS.png" srcset=" enterJS-1x.png 1x, enterJS-2x.png 2x, enterJS-3x.png 3x " />
  59. RESPONSIVE IMAGES <img src="enterJS.png" srcset=" enterJS-300.png 300w, enterJS-600.png 600w, enterJS-1200.png

    1200w " /> <img src="enterJS.png" srcset=" enterJS-1x.png 1x, enterJS-2x.png 2x, enterJS-3x.png 3x " />
  60. #PROTIP ๐Ÿ’ก Lazy-loading iframes can lead to 2-3% median data

    savings, 1-2% FCP reductions, and 2% FID improvements at the 95th percentile. โ€”โ€‰Chrome teamโ€™s research, 2019
  61. NATIVE SCHEDULER โ† A MORE ROBUST SOLUTION FOR SCHEDULING TASKS

    โ† CONTROL AND SCHEDULE PRIORITIZED TASKS IN A UNITED AND FLEXIBLE WAY โ† INTEGRATED DIRECTLY INTO THE EVENT LOOP โ† ALIGNED WITH THE WORK OF THE REACT TEAM AND IN COOPERATION WITH GOOGLE, W3C AND OTHERS
  62. NATIVE SCHEDULER scheduler.postTask() SCHEDULE AND CONTROL PRIORITIZING TASKS. scheduler.wait() YIELD

    AND RESUME AFTER SOME AMOUNT OF TIME OR PERHAPS AFTER AN EVENT HAS OCCURRED. scheduler.yield() BREAK UP LONG TASKS BY YIELDING TO THE BROWSER AND CONTINUING AFTER BEING RESCHEDULED. isInputPending() DETERMINE IF THE CURRENT TASK IS BLOCKING INPUT EVENTS.
  63. โ€ฆAND MUCH MORE! โ† CSS TRICKS (E.G. font-display: swap AND

    will- change) โ† IMPORT ON VISIBILITY (USING AN IntersectionObserver) โ† CANVAS + WORKERS = OffscreenCanvas
  64. โ€ฆAND MUCH MORE! โ† AVOID THE INITIAL HTTP TO HTTPS

    REDIRECTS SO THAT PAGES LOAD FASTER USING HTTP STRICT TRANSPORT SECURITY (HSTS) โ† SEND DATA WITHOUT EXTRA ROUND TRIPS WITH QUIC
  65. MOVE FAST & BREAK NOTHING โ„ข const Video = lazy(()

    = > import("./Video")); const Preview = lazy(() = > import("./Preview")); const networkInfo = useNetworkStatus(); const { With, Switch, Otherwise } = usePatternMatch(networkInfo);
  66. MOVE FAST & BREAK NOTHING โ„ข <Suspense fallback={<div>Loading . .

    . </div>}> <With unsupported> <NetworkStatus networkInfo="unsupported" /> <Video /> </With> <With effectiveConnectionType="2g"> <NetworkStatus networkInfo="2g" /> <Preview /> </With> </Suspense>
  67. WEB PERFORMANCE APIS THAT YOU (PROBABLY) NEVER KNEW EXISTED Which

    browsers are visiting our app? โ€”โ€‰APP DYNAMICS REPORT
  68. #REALITYCHECK ๐Ÿ˜ณ Phone users experience slow First Input Delay on

    7x more websites. โ€”โ€‰Web Almanac By HTTP Archive, 2021
  69. British Psychology Society, 2009 40% of Brits reported that they

    had become physically violent toward their computers.
  70. Radware, 2013 A 500ms delay resulted in up to a

    26% increase in frustration and up to an 8% decrease in engagement.
  71. Ericsson ConsumerLab, 2015 Delayed web pages caused a 38% rise

    in mobile users' heart rates โ€” equivalent to the anxiety of watching a horror movie alone.
  72. BUSINESS OUTCOMES โ€”โ€‰AKAMAI AND CHROME RESEARCH, 2017 โ† LONG TASKS

    DELAYED TTI โ† AS FIRST-PAGE LONG TASK TIME INCREASED, OVERALL CONVERSION RATES DECREASED โ† MOBILE HAD UP TO หœ12X LONGER LONG TASKS โ† OLDER DEVICES COULD BE SPENDING HALF OF THEIR LOAD-TIME ON LONG TASKS
  73. WEB PERFORMANCE APIS THAT YOU (PROBABLY) NEVER KNEW EXISTED ALWAYS

    TRY TO CORRELATE BUSINESS METRICS WITH PERFORMANCE. #1 of 6
  74. WEB PERFORMANCE APIS THAT YOU (PROBABLY) NEVER KNEW EXISTED DON'T

    TAKE FAST NETWORKS, CPUS AND RAM FOR GRANTED. #2 of 6
  75. WEB PERFORMANCE APIS THAT YOU (PROBABLY) NEVER KNEW EXISTED GET

    RID OF THE NOISE IN YOUR METRICS. #5 of 6
  76. WEB PERFORMANCE APIS THAT YOU (PROBABLY) NEVER KNEW EXISTED THERE'S

    NO SILVER BULLET. IDENTIFY YOUR CORE METRICS. #6 of 6